L1 control signaling for UTRAN HSDPA

ABSTRACT

A Level-1 (L1) signaling flag is mapped to unused (invalid) bit sequences in Part 1 of the HS-SCCH—that is, Part 1 bit encodings that are not defined in the UTRAN specifications—and a corresponding L1 command is encoded in Part 2. This allows UE to detect early that the HS-SCCH is pure L1 signaling, and the UE may avoid wasting power by not processing an accompanying HS-PDSCH. Alternatively, in CPC HS-SCCH-less mode, the UE may blind decode the HS PDSCH. In one embodiment, a general DRX mode is defined and controlled via L1 signaling. In one embodiment, a UE acknowledgement improves the L1 signaling accuracy. In one embodiment, a L1 signal and UE acknowledgement protocol are utilized to “ping” a UE.

This application claims priority to Swedish application SE 0700287-6filed Feb. 5, 2007 and Swedish application SE 0700838-6-6 filed Mar. 27,2007.

TECHNICAL FIELD

The present invention relates generally to wireless communications andin particular to improved L1 signaling between a UTRAN network and UserEquipment.

BACKGROUND

The present invention relates to low level signaling in a UMTSTerrestrial Radio Access Network (UTRAN). A UTRAN wireless communicationnetwork 10 is depicted in FIG. 1. The UTRAN network comprises a CoreNetwork (CN) 12, a plurality of Radio Network Controllers (RNC) 14, andplurality of Node Bs 16, also known in the art as Base Stations, eachproviding communication services to one or more User Equipment (UE) 18,also known as mobile stations, across an air interface within a cell orsector 20. The CN 12 may be communicatively coupled to other networkssuch as the Public Switched Telephone Network (PSTN), the Internet, aGSM network, or the like, and the UTRAN network 10 provides datatransfer between these external networks and UE 18.

High-Speed Downlink Packet Access (HSDPA) introduced numerous featuresinto the UTRAN network 10, including broadcasting data packetsthroughout the cell 20 on a High Speed Downlink Shared Channel (HS-DSCH)and control information on a High Speed Shared Control Channel(HS-SCCH). HSDPA utilizes channel-dependent scheduling, whereby datadirected to each UE 18 is scheduled for transmission on the sharedchannel when the instantaneous channel quality to that UE 18 is high. Tosupport this feature, which requires rapid response to changing channelconditions, scheduling is moved from the RNC 14 into the Node B 16, anda shorter Transmission Time Interval (TTI) of 2 msec (or 3 slots) isdefined.

Similarly, fast rate control and higher order modulation (HOM)—referredto together as Adaptive Modulation and Coding (AMC)—are used for linkadaptation, wherein the data rate of each transport block and themodulation scheme are varied in response to channel conditions to thetarget UE 18 (and the capability of the UE 18). In addition, HSDPAemploys a hybrid-ARQ (HARQ) acknowledgement scheme, wherein soft valuesof unsuccessfully decoded transport blocks are retained and combinedwith the soft decoding results of each retransmission. This allows forincremental redundancy, reducing the need for further retransmissions.The scheduling, AMC, and HARQ functions must all be close to the radiointerface on the network side, and hence have been migrated to the NodeB 16.

Multiple-Input, Multiple-Output (MIMO) technology is another HSDPAfeature being incorporated in to the UTRAN standards. In particular,MIMO may be combined with HOM in a forthcoming UTRAN standard revision.Such features have traditionally been controlled by the RNC 14, viaLayer 3 (L3) signaling. A fundamental deficiency of RNC 14 control ofHSDPA features is high latency, relative to the TTI length. If certainfeatures or modes should optimally be switched on/off frequently, theoverhead in higher layer signaling becomes a major obstacle. Indeed, ifmode switching is required frequently enough, higher layer signaling isnot an option.

Another example of a HSDPA feature that suffers from excessive latencyunder RNC 14 control is Discontinuous Transmission (DTX) and/orDiscontinuous Reception (DRX) modes in UE 18. Release 7 of the UTRANspecification defines “continuous connectivity for packet data users,”or simply, Continuous Packet Connectivity (CPC). CPC enhances systemcapacity to support a very large number of packet-oriented users byreducing signaling overhead, uplink interference, and downlinktransmission power. One feature of CPC mode is uplink DTX, to reduceuplink interference and conserve UE battery power (due to power control,uplink DTX implies downlink DRX). Furthermore, a DRX mode independent ofCPC would be beneficial, to relieve UE 18 from the requirement ofmonitoring every HS-SCCH transmission for L1 signaling. ACPC-independent DRX/DTX mode would ideally include a provision foracknowledgement by the UE 18. For example, the network 10 should notschedule downlink data to a UE 18 in DRX, that has been sent a commandto terminate the DRX mode, until it receives an acknowledgement from theUE 18 that DRX mode is actually terminated, and the UE 18 is monitoringHS-SCCH.

In CPC mode, UE 18 DRX/DTX is controlled by certain bit sequences in aTransport Block Size (TBS) field of an HS-SCCH transmission (that is,bit sequences that are not valid TBS values). However, the DRX/DTX bitsare in Part 2 of the HS-SCCH, which requires a UE 18 to detect theentire HS-SCCH to deduce if the TBS field is valid (and accompanyingdata will be found in a HS-PDSCH transmission) or if a CPC command isencoded into the TBS field (in which case no data is transmitted, andthe HS-SCCH is pure L1 signaling). Since the TBS field is in Part 2, theUE 18 must process a HS-PDSCH in either case—which is wasted power inthe latter case.

Another problem with this particular means of L1 signaling of DRX/DTXmode occurs with respect to another CPC feature: HS-SCCH-less operation,in which data are transmitted without the accompanying controlinformation to reduce downlink interference. UE 18 first look forHS-SCCH-accompanied HS-PDSCH transmissions. If none is detected, the UE18 should attempt to receive HS-SCCH-less HS-PDSCH transmissions, usingblind decoding to discover the coding rate. Part 1 of a HS-SCCHtransmission including only DRX/DTX L1 control signaling isindistinguishable from Part 1 of a HS-SCCH transmission accompanying aHS-PDSCH transmission (the TBS field being in Part 2). Accordingly, upondetecting HS-SCCH, UE 18 have no choice but to assume there will be aHS-SCCH-accompanied HS-PDSCH transmission. This precludes the UE 18 fromprocessing the HS-PDSCH transmission as a HS-SCCH-less one, thuspreventing the network 10 from simultaneously transmitting DRX/DTX L1control signaling on HS-SCCH and data in a HS-SCCH-less HS-PDSCH. Usingthe defined TBS bit sequences for transmitting a CPC-independent DRX/DTX(de)activation signal suffers the same problems.

SUMMARY

According to various embodiments described and claimed herein, an L1signaling flag is mapped to unused (invalid) bit sequences in Part 1 ofthe HS-SCCH—that is, Part 1 bit encodings that are not defined in theUTRAN specifications—and a corresponding L1 signaling command is encodedin Part 2. This allows UE 18 to detect early that the HS-SCCH is pure L1signaling, and the UE 18 may avoid wasting power by not processing anaccompanying HS-PDSCH. Alternatively, in CPC HS-SCCH-less mode, the UE18 may blind decode the HS-PDSCH. In one embodiment, the L1 signalingflag indicates that CPC DRX mode commands are encoded in Part 2. Inanother embodiment, a general (i.e., non-CPC) DRX mode is defined, andcontrolled via L1 signaling. In one embodiment, a UE 18 acknowledgementimproves the L1 signaling accuracy. In one embodiment, a L1 signal andUE 18 acknowledgement protocol are utilized to “ping” a UE 18.

Encoding an L1 signaling flag into unused Part 1 bit encodings in theHS-SCCH provides UE 18 with advanced notice that the HS-SCCH is for L1signaling and does not accompany HS-PDSCH data. It also enables thenetwork 10 to simultaneously transmit L1 signaling commands andHS-SCCH-Iess data packets. Transmitting the L1 signals by a scheduler inthe Node B 16 improves response time and reduces latency over comparableL3 signaling. A non-CPC DRX mode provides for UE 18 power savings, andL1 DRX signaling with UE 18 acknowledgements may implement a pingoperation.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a functional block diagram of a UTRAN wireless communicationnetwork.

FIG. 2 is depicts HS-SCCH and HS-PDSCH frame structure and timing.

FIG. 3 is a flow diagram of a method of pinging a UE in a UTRAN network.

DETAILED DESCRIPTION

FIG. 2 depicts the frame structure and relative timing of the HS-SCCHand HS-PDSCH. The HS-SCCH is a fixed rate (60 kbps, SpreadingFactor=128) downlink physical channel used to carry downlink signalingrelated to HS-DSCH transmission. This provides timing and codinginformation thus allowing the UE 18 to listen to the HS-PDSCH at thecorrect time and using the correct codes to successfully decode UE 18data. The HS-SCCH is transmitted two slots in advance of thecorresponding HS-DSCH TTI. The HS-SCCH is divided into two parts, andincludes the following control information (when MIMO is notconfigured):

Part 1:

UE identity (16 bits): Xue

Channelization-code-set (7 bits): Xccs

Modulation scheme information (1 bit): Xms

Part 2:

Transport-block size information (6 bits): Xtbs

Hybrid-ARQ process information (3 bits): X hap

Redundancy and constellation version (3 bits): X rv

New data indicator (1 bit): X nd

The HS-PDSCH is a variable rate (SF=16) physical downlink shared channelused to carry data packets directed to one or more specific UE 18. TheHS-PDSCH has a fixed Spreading Factor of 16, a static TTI length of 3slots (2 msec), a fixed CRC of 24 bits, and error correction using ⅓turbo coding. Data may be modulated by QPSK or 16 QAM, as specified inthe associated HS-SCCH.

As discussed above, it is known to utilize unused (invalid) encodings ofthe TBS field of HS-SCCH Part 2 to carry L1 signaling—specifically,DRX/DTX commands in CPC mode. However, this field is in Part 2, leavinginsufficient time for the UE to decode the TBS field prior to receivingand processing—or not—the HS-PDSCH.

Some bit sequences in Part 1 of the HS-SCCH are not defined in the UTRANspecifications. According to one or more embodiments, an L1 signalingflag is mapped to these unused (invalid) Part 1 bit sequences, and L1signaling is encoded in Part 2. By encoding the L1 signaling flag intoPart 1, a UE 18, upon first receiving a HS-SCCH transmission, canimmediately ascertain whether the HS-SCCH transmission is dedicated toL1 signaling. This presents several significant advantages over theprior art.

In particular, if for the current CPC DRX/DTX L1 signaling, an L1 flagis encoded in Part 1, UE 18 decoding a HS-SCCH Part 1 are assured thatif Part 1 decodes to their Xue, and valid Xccs and Xms values, anaccompanying HS-PDSCH transmission contains data and the UE 18 mustprocess it. Alternatively, if the UE 18 detects the L1 signaling flag inPart 1, it may safely ignore a succeeding HS-PDSCH transmission or, ifHS-SCCH-less mode is enabled, it may blind decode the HS-PDSCHtransmission in parallel with interpreting and responding to the L1signaling in Part 2. This allows the UTRAN network 10 to simultaneouslysend L1 signaling and HS-SCCH-less data packets to a UE 18—functionalitythat is not possible in prior art network implementations.

The L1 DRX/DTX (de)activation signal(s) need not be confined to CPC modeDRX/DTX. Release 7 of the UTRAN specification defines an EnhancedCELL_FACH state. In CELL_FACH state, no dedicated physical channel isallocated to the UE in Frequency Domain Duplex (FDD) systems (in TimeDivision Duplex (TDD) mode, one or several USCH or DSCH transportchannels may have been established). The UE 18 continuously monitors aForward Access Channel (FACH) in the downlink, and is assigned a defaultcommon or shared transport channel in the uplink (e.g., RACH) on whichit may initiate access to the network 10.

It would be advantageous to UE 18 power consumption if the UE 18 was notrequired to continuously monitor HS-SCCH. According to one embodiment, ageneral DRX mode is defined that controls UE 18 reception behavior. Forexample, a DRX activation period may be defined during which the UE 18may switch off its receiver circuits to conserve battery power. At theexpiration of a predefined DRX activation cycle, the UE 18 activates itsreceiver to monitor HS-SCCH transmissions for a short period todetermine if data is scheduled for that UE 18. Either or both of the DRXactivation period and the DRX deactivation period durations may bespecified in the L1 signaling (for example, encoded into HS-SCCH Part2), or may be configured in advance by higher layer applications.

Some data transmissions will be delayed when DRX mode is enabled, as thenetwork 10 must wait for the next occasion of UE 18 DRX deactivationprior to scheduling data for transmission. The mean delay will dependprimarily on the length of the DRX activation period. Those of skill inthe art, given the teachings of the present application, will be able todetermine the appropriate trade-off between UE 18 battery savings andacceptable delay in data transmissions, for a given implementation.

While the RNC 14 may control the general DRX mode for UE 18 via L3signaling, the L3 signaling adds significant overhead and latency,particularly where the network 10 requires an acknowledgement from theUE 18 of its DRX state prior to transmitting data to it. Furthermore,for the same reason scheduling, AMC, and HARQ were moved to the Node B16—that it has more detailed knowledge of the instantaneous channelconditions, available power, available codes, and otherparameters—transmission of L1 DRX signaling in Part 1 of HS-SCCH ispreferably performed by the Node B 16, in particular, by the schedulerin the Node B 16.

Regardless of the signaling mechanism used for moving the UE 18 betweendifferent DRX modes, it should be noted that a signaling failure couldhave serious negative impacts on user experience and system performance.If the UE 18 erroneously activates DRX mode, data loss may occur whenthe Node B 16 schedules data to the UE 18 while the UE 18 is notmonitoring HS-SCCH. Alternatively, if the UE 18 erroneously deactivatesDRX, its battery consumption will be unnecessarily high. Signalingfailures should thus be minimized. One known method to reduce signalingfailure is via a reliable acknowledgement mechanism.

In one embodiment, the UE 18 acknowledges a general (i.e., non-CPC) DRXmode command by transmitting an acknowledgment on the Random AccessChannel (RACH), which is the uplink channel available in CELL_FACHstate. The acknowledgment must identify the UE 18—a requirement of anyRACH transmission—and additionally includes a unique code indicatingthat the transmission acknowledges receipt of the corresponding DRXcommand. In one embodiment, the acknowledgment is captured directly bythe Node B 16. In another embodiment, the acknowledgment is received bythe RNC 14, which then informs the Node B 16 of it. The latterembodiment may be viewed as an L1 signal encapsulated in an L3 message.While there is no difference between these two embodiments in principle,as a practical matter, direct capture by the Node B 16 will result inthe lowest latency and fastest response.

An additional advantage of a general DRX mode via L1 signaling and DRXacknowledgement by UE 18 is that the Node B 16 may make use of thesignaling protocol to implement a “ping” operation to verify theoperative presence of a UE 18. This method 100 is depicted in flowdiagram form in FIG. 3. At any time, if a UE 18 is in DRX disabled mode(i.e., constantly monitoring HS-SCCH), or during a deactivation period,if the UE 18 is in DRX enabled mode (i.e., only periodically monitoringHS-SCCH), the Node B 16 may send the UE 18 a DRX L1 signal commandingthe UE 18 to (preferably) the same DRX mode (block 102). If the Node B16 receives an acknowledgment (block 104), it knows the UE 18 is in thecell 20, and within the range of the HS-SCCH transmission power level(block 106). If the Node B 16 does not receive an acknowledgement of theL1 signal (block 104), it may increase the HS-SCCH transmission powerlevel (block 108) and resend the DRX command (block 110). If the Node B16 again does not receive an acknowledgement the L1 signal (block 112),it may assume the UE 18 has been turned off or has left the cell 20(block 114). Of course, the increased-power attempt to ping the UE 18 isoptional, as indicated by the dashed-line path from block 104 to block114 in FIG. 3. Note that the Node B 16 should take care that, if thesignaling is for pinging a UE 18 and not a DRX mode change, it shouldideally only command the UE 18 to its then-current DRX mode.

While an L1 signaling flag in Part 1 of HS-SCCH has been describedherein with respect to general DRX mode commands, the present inventionis not so limited. In general, any command may be encoded into Part 2 ofHS-SCCH, and indicated by an L1 signaling flag in Part 1, such ascommands controlling CPC, HOM, MIMO, or any other UE 18 mode or feature.By placing an L1 signaling flag in Part 1, the UE 18 may quicklydistinguish a pure L1 signaling HS-SCCH from an HS-SCCH accompanying aHS-PDSCH. This allows the UE 18 to safely ignore the HS-PDSCH, oralternatively to blind decode an HS-SCCH-less HS-PDSCH.

The present invention may, of course, be carried out in other ways thanthose specifically set forth herein without departing from essentialcharacteristics of the invention. The present embodiments are to beconsidered in all respects as illustrative and not restrictive, and allchanges coming within the meaning and equivalency range of the appendedclaims are intended to be embraced therein.

What is claimed is:
 1. A method of transmitting level-1 signaling from aNode B to User Equipment (UE) in a UTRAN wireless communication network,comprising: encoding an L1 signaling flag in Part 1 of a High SpeedShared Control Channel (HS-SCCH), wherein the L1 signaling flagindicates that Part 2 of the HS-SCCH includes an L1 DiscontinuousReception (DRX) command to be decoded by a UE receiving the HS-SCCH;encoding the L1 DRX command indicated by the L1 signaling flag in Part 2of the HS-SCCH; transmitting the HS-SCCH to one or more UEs; monitoringa Random Access Channel (RACH) for an acknowledgement of the L1DRXcommand from a User Equipment (UE); and receiving the acknowledgement ofthe L1 DRX command from the UE on the RACH.
 2. The method of claim 1wherein encoding an L1 signaling flag in Part 1 of a HS-SCCH comprisesmapping the L1 signaling flag to an unspecified encoding of the HS-SCCHPart
 1. 3. The method of claim 1 wherein the L1 signaling flag alsoindicates that Part 2 of the HS-SCCH also includes an L1 signal thatcontrols the use of multiple-input, multiple output (MIMO) modes in theUE.
 4. The method of claim 1 wherein the L signaling flag also indicatesthat Part 2 of the HS-SCCH also includes an L1 signal that controls theactivation or deactivation of Continuous Packet Connectivity (CPC) modein the UE.
 5. The method of claim 1 wherein transmitting the L1DRXcommand, and a presence or absence of a UE acknowledgement, comprises aping operation that ascertains the presence of the UE in a coverage areadefined by the HS-SCCH transmission power level.
 6. The method of claim5 wherein, if the transmitted L1 DRX command used for a ping may alter amode or state of the UE, the signal commanding the UE to its currentmode or state is transmitted.
 7. The method of claim 5 furthercomprising, if no UE acknowledgement is received, retransmitting the L1DRX command at a higher HS-SCCH transmission power level.
 8. A method ofcontrolling Discontinuous Reception (DRX) in UE in a UTRAN wirelesscommunication network, comprising: encoding an L1 signaling flag in Part1 of a High Speed Shared Control Channel (HS-SCCH), wherein the L1signaling flag indicates that Part 2 of the HS-SCCH includes an L1Discontinuous Reception (DRX) command to be decoded by a UE receivingthe HS-SCCH; encoding the L1 DRX command in Part 2 of the HS-SCCH;transmitting the HS-SCCH to a UE in a CELL_FACH state, that is not inContinuous Packet Connectivity (CPC) mode, to activate or deactivate aDRX mode in the UE; and receiving from the UE an acknowledgement of theL1 DRX command.
 9. The method of claim 8 wherein encoding theL1signaling flag in Part 1 of a HS-SCCH comprises mapping the L1signaling flag to an unspecified encoding of the HS-SCCH Part
 1. 10. Themethod of claim 8 wherein transmitting the L1 DRX command to the UEcomprises encapsulating the L1 DRX command in an L3 message, andtransmitting the L3 message to the UE.
 11. The method of claim 8,further comprising concluding, on failure to receive an acknowledgementof the L1 DRX command from the UE, that the UE is inoperative or outsidethe range defined by the power level of the L1 DRX command transmission.12. A UTRAN wireless communication network, comprising: a Node Boperative to: transmit an L1 signal to a User Equipment (UE) by encodingan L1 signaling flag into an unused bit encoding in Part 1 of a HighSpeed Shared Control Channel (HS-SCCH) transmission, wherein the L1signaling flag indicates that Part 2 of the HS-SCCH includes an L1Discontinuous Reception (DRX) command to be decoded by the userequipment (UEs), and encoding the L1 DRX command in Part 2 of theHS-SCCH, and transmitting the HS-SCCH to the UE; and receive from the UEan acknowledgement of the L1 DRX command.
 13. The network of claim 12,wherein the Node B receives the L1 signal acknowledgement from the UE ona Random Access Channel (RACH).
 14. The network of claim 12, wherein theL1 DRX command is independent of a Continuous Packet Connectivity (CPC)mode.
 15. The network of claim 14 wherein the Node B is furtheroperative to ping a UE by transmitting the L1 DRX command to enter thecurrent DRX mode of the UE and receiving a UE acknowledgement.